Is it [possible to remove the I2C pull-up resistors] "by hand" (I do have that fine tip for soldering but not much experience with miniature soldering)?
I think I've reverse-engineered the schematic for your board (it would be easier with the board in my hands) - and then I found a schematic online for a similar (though not identical) breakout board to yours, which fits with my analysis.
So I'm fairly confident, but you have the board in your hands and I don't, so please check my assumptions.
The bad news is that, as you know, your board wasn't designed to allow easy disconnection of the I2C pull-ups. Although it's easy to disconnect the pull-up from SDA, it's a little harder for SCL. My approach requires a sharp scalpel to cut traces and a small jumper wire needs to be added.
I've found a slightly more in-focus photo of your board from one of the many Ebay sellers, so I've marked the changes on there:
There are a number of ways to approach your requirement. I'm assuming that you want to make minimal modifications to the breakout boards.
Looking at the vertical green line
4: I believe the two 10k resistors in the resistor pack to the left of that line, both have their upper connections to the 3.3V from the 3-pin regulator immediately above on the PCB. Think of those as the "internal I2C pull-ups". You don't want to disconnect those.
The two 10k resistors in the resistor pack to the right side of green line
4 both have their upper connections to the external
VIN pin. Think of those as the "external I2C pull-ups" and those are the ones you do want to disconnect.
Although not easy to see in any of the photos so far, I found another photo of this breakout board that showed the 6-pin SOT323 package device had the top mark
702. That fits with the package being a dual N-channel MOSFET (similar to two 2N7002 MOSFETs in one package). As an example, the GSM7002T is such a device, and has the top code
Provided the few critical parameters (especially Vgs) are suitable, then other dual N-channel MOSFET devices could also be used in that location, so I expect there are a variety of other top marks on those devices used on the various breakout boards. The purpose of that device is as a typical level-changer (level translator) for the two I2C signals, since according to the VL53L0X datasheet, it should not be connected directly to an I2C bus which is pulled-up to anything above 3.5V e.g. a 5V I2C bus.
- To disconnect the "external I2C pullups" you need to:
- Cut the track at point
1 to disconnect the external pull-up to
- Cut the track at point
2 to disconnect the external pull-up to
- Solder an insulated jumper wire as shown for connection
3, between the Drain
D1 of the dual N-channel MOSFET, and the SCL header pin hole.
Then you can add one suitable pull-up resistor to each of the two I2C signals, as appropriate for the whole I2C bus. Job done!
Later, I found that Pololu make a VL53L0X breakout board and they supply a schematic diagram:
That schematic nicely shows the use of the N-channel MOSFETs as level-changers. It is not completely accurate for your board, but the differences are fairly small, e.g.:
The header pinout is obviously different.
Your board probably has a 3.3V regulator (this is based on the top codes that I saw on various other Ebay listings - I can't read the regulator's top code on your photos); the Pololu board has a 2.8V regulator.
Instead of discrete resistors on the Pololu board, 4 resistors are replaced by the resistor pack on your board.
The Pololu board has 47k pull-ups on
GPIO1 and 1k series resistors in both signals; your board has 10k pull-ups and no series resistors.
From a quick comparison:
- Pololu R1 = 4th resistor from the left in your 10k resistor pack
- Pololu R2 = 3rd resistor from the left in your 10k resistor pack
- Pololu R3 = 2nd resistor from the left in your 10k resistor pack
- Pololu R4 = leftmost resistor in your 10k resistor pack
- Pololu R5 & R6 = separate 10k resistors near the
GPIO1 header pin holes on your board.
I have no association with Pololu, but their documentation is always far above the near-zero information from Ebay, Ali Express and Amazon sellers etc., so I have been a happy buyer of their products.